Drive line noise mystery? Solved

[alborz]

I noticed when the air bags for drive axles are empty completely and the chassis sits on the u-bolt sales, the very rear axle touches the chassis but the front drive axle does not. there is about 1/2" or more distance between the saddle and chassis. and also when the air bags are filled the rotation angel of axle is higher on front axle compared to rear axle. So I'm thinking that when the truck is coasting , there is a flip flap or swing play on rear axle rotation and constantly change of angle which in turn change the angle driveshaft between two rear axles.
do you think this theory is any close to reality?
why not four sales touch the chassis? and how can I fix that?
thanks in advance

[Chamberpains]

I don't know if all trucks sit on top of the stopping blocks when the air is out on level ground. It may be designed that the front axle stop blocks touch when you're on, say, a curb or Hill or a pothole. Something like that. You could always call the truck manufacturer and ask. Also give a thorough check to make sure a bracket isn't bent or a shock isn't stuck or a spring isn't bent. Look for something that is causing that axle to sit weird and not have its full length of travel.

[alborz]

I'm trying to see if other peterbilt 387s leaf springs are flat or arc shape "between the hanger to the chasee and where it sits on the top of the axles " on all four springs.
I noticed two of my springs are flat and two are arc shaped.
So Please those who have Peterbilt 387 inspect their rear axles and note their air leaf springs and Kindly report back here their findings.

thank you in advance for your help

[Nilao]

I need more information. What suspension is it? Peterbilt low low air leaf, low air leaf, or other proprietary peterbilt suspension type? They're all different spring configurations.

[alborz]

(04-25-2018 )Nilao Wrote:  I need more information. What suspension is it? Peterbilt low low air leaf, low air leaf, or other proprietary peterbilt suspension type? They're all different spring configurations.

Low air and "z" shape spring

[Nilao]

the front axle spring on my friends 387 has a very slight arch, the rear axle spring has a pronounced upward arch in comparison.

[alborz]

(04-26-2018 )Nilao Wrote:  the front axle spring on my friends 387 has a very slight arch, the rear axle spring has a pronounced upward arch in comparison.

Does your friend’s truck chassis touch the top of the saddle on axles when air bags empty?

[Nilao]

No..he has approx 4 inches of clearance from frame to axle.

[alborz]

I think the guy at the shop put the rear/ rear spring for the front and the one for the front to the rear
How can I figure it out?
Anybody knows a link, source, or something?